The present invention relates to an ink jet printer with an ink ejection head in which an electrostrictive vibrator is mounted to be driven to eject ink and separate a droplet therefrom. More particularly, the present invention relates to an ink viscosity regulation apparatus which, when a predetermined voltage level is exceeded by a vibrator drive voltage level which separates a droplet from the ejected ink at the shortest distance from the head, supplies a diluent to the ink to thereby control the ink to an appropriate viscosity.
In a known type of ink jet printer, ink inside a head is effected by an electrostrictive vibrator or the like to be ejected from a head and separated into a string of droplets. This type of ink jet printer has a problem that undesirable microscopic ink droplets, generally called "satellites", are produced independently of expected droplets depending upon the distance for separation. The development of satellites is related with various parameters such as the drive voltage, i.e., nozzle drive amplitude, and the pressure and temperature of ink. Because the satellites disturb data reproduction on a recording medium, it is a requisite to set up a nonsatellite or satellite-free range during data reproduction. This in turn requires that the head be actuated by an optimum drive voltage and that the ink be properly diluted to have an adequate viscosity. The dilution is to compensate for an increase in viscosity which generally occurs during circulation of the ink due to evaporation of water and entails the liability of satellites due to the resulting change in the distance for ink separation.